USB: fix out-of-bounds in usb_set_configuration

Andrey Konovalov reported a possible out-of-bounds problem for a USB interface
association descriptor.  He writes:
	It seems there's no proper size check of a USB_DT_INTERFACE_ASSOCIATION
	descriptor. It's only checked that the size is >= 2 in
	usb_parse_configuration(), so find_iad() might do out-of-bounds access
	to intf_assoc->bInterfaceCount.

And he's right, we don't check for crazy descriptors of this type very well, so
resolve this problem.  Yet another issue found by syzkaller...

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/linux/usb/ch9.h

@@ -780,6 +780,7 @@ struct usb_interface_assoc_descriptor {
 	__u8  iFunction;
 } __attribute__ ((packed));
 
+#define USB_DT_INTERFACE_ASSOCIATION_SIZE	8
 
 /*-------------------------------------------------------------------------*/